Hardening by a photo (active energy rays)-sensitive polymerization initiator (hereinafter may be abbreviated only as a photo-polymerization initiator) (hereinafter the hardening may be abbreviated only as photo-hardening) has many advantages that hardening can be carried out at low temperature and for a short time, and can perform fine pattern formation and the like, comparing with hardening by a thermal-sensitive polymerization initiator (hereinafter may be abbreviated only as a thermal polymerization initiator) (hereinafter the hardening may be abbreviated only as thermal-hardening), therefore, it has been widely used in the application of surface processing such as coating materials, printing inks, dental materials, resists.
Photo-polymerization initiators to be used in the photo-hardening technology can be classified as 3 groups consisting of a photoradical generator, a photoacid generator, and a photobase generator according to the generated active species. The photoradical generator is a photo-polymerization initiator typically represented by acetophenone and the like which generates radical species when irradiated with light (active energy rays), and has been hitherto widely used. However, the radical species have a property of deactivating by oxygen in air, therefore, there is a disadvantage that the polymerization reaction is prohibited in the presence of oxygen, and hardening is consequently inhibited. Accordingly, when a thin film is hardened by using the photoradical generator, special device, by which oxygen is blocked in the air, is required. In addition, since the photoacid generator is the photo-polymerization initiator which generates an acid when irradiated with light (active energy rays), it has an advantage that it is not affected by inhibition due to oxygen, consequently, various photoacid generators have been used in practice since the latter half of the '90. However, when the generated acid by irradiated with light (active energy rays) is remained within system even after hardening, the problems that performance deterioration based on the denaturation of the hardened film and corrosion of the substrate in the semiconductor field and the like are pointed out. On the other hand, since the photobase generator is the photo-polymerization initiator which generates a base when irradiated with light (active energy rays), it has an advantage that it has not been affected by inhibition due to oxygen in the air, in addition, corrosion problem or denaturation of hardened film is hardly occurred. Therefore, this is the photo-polymerization initiator in which research and development thereof has been actively performed lately.
As such photobase generators, there are known various photobase generators, for example, such as a carbamate type (urethane type) photobase generator (for example, Patent Literature 1 and the like), an α-aminoketone type photobase generator (for example, Patent Literature 2 and the like), a quaternary ammonium type photobase generator (for example, Patent Literature 3, 4 and the like), an O-acyloxime type photobase generator (for example, Patent Literature 5 and the like).
On the other hand, an epoxy resin which is used as a photo-hardening resin has been hitherto hardened by graft polymerizing the epoxy resin by an acid generated from the acid generator by the action of light (active energy rays) under the coexistence of the resin and the acid generating-compound such as a photoacid generator. However, as mentioned above a little, when the acid is remained within the system even after hardening, problems of denaturing the hardened film or corroding the substrate due to the residual acid are occurred. For this reason, as the hardening method without occurring these problems, the method that the epoxy resin is hardened with a base, that is, the hardening of the epoxy resin by using the photobase generator is widely researched. However, at present, it is difficult situation of practical use due to the lack of sensitivity of the epoxy resin for the photobase generator. For this reason, research of a photo-hardening resin composition using an episulfide resin instead of the epoxy resin as the photo-hardening resin has been carried out (for example, Patent Literature 4 and the like). However, episulfide compounds as the episulfide resin precursor show the absorption in the vicinity of 300 nm wavelength. Therefore, when the photobase generator which has the same photosensitive range for the light (active energy rays) centered in the vicinity of 300 nm wavelength was used, there was a problem that generation efficiency of the base from the photobase generator decrease.
Under these circumstances, there has been expected the development of the photobase generator which eliminates overlap with the photo-absorption range of episulfide compounds, or even when overlapped, does not decrease the generation efficiency of the base, and can generate base efficiently, that is, the development of the photobase generator which has high sensitivity to longer wavelength light (active energy rays) comparing with the photosensitive range of the conventional photobase generator, and efficiently generates base when irradiated with the long wavelength light (active energy rays).